1. Field of the Invention
This invention relates to protective housings for electrical wiring devices, and, more particularly, to a snap-on wiring device cover for protecting electrical and mechanical components of such devices.
2. Description of the Prior Art
Good trade practice, as well as the Underwriters Laboratories, Canadian Standards Association and other safety Standards require that intricate electrical and mechanical components of wiring devices have sufficient protection from external influences. Such protection includes physical separation from the building wire when a wiring device is installed in a wall box, protection of the mechanism from entrance of dust or similar foreign materials and protection from abuse or misuse in handling, shipping and during installation.
For wall mounted wiring devices, such as dimmers, motor controls, timers, switches, etc., the device assembly typically consists of a mechanism mounted to a plate for attachment to a switch box. In order to protect the components and the mechanism of the device from dust or dirt contamination or mechanical abuse, a cover of suitable material is fastened over the device components and to the plate. Conventionally, the cover was fastened to the plate with rivets, screws or heat staked projections on the cover. The riveted connection was a single use type, so that if the cover were removed from the plate, the fastener would be destroyed. With the screw type of fastener, the fit of the screw in the tapped hole would become less secure and the lesser screw thread engagement would cause the fastening to be inadequate. Removal of a cover employing the heat staked tabs destroyed the tabs and rendered the cover useless. In standard installations, a wall plate is fastened over the front plate of the wiring device to provide electrical insulation and a more pleasing appearance. Standard wall plates often have stiffening ribs running horizontally and/or vertically on the back side of the plate. Any fastening mechanism which protrudes beyond the front plate of the bracket mounting surface can interfere with the wall plate ribs. Also, as a wall plate is fastened over the wiring device, the ribs on the wall plate exert force on the snaps which tend to push the cover from the bracket. Any part of the fastening mechanism holding the wiring device cover to the bracket mounting surface which projects beyond the mounting surface can interfere with the placement of the wall plate and is, therefore, unsatisfactory. Furthermore, the requirement for separate fastening devices for the covers adds to the cost of assembly and installation as well as the speed of assembly of the wiring devices.